Electric Power Steering Active Return Control
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Solution Overview
Problem
Conventional electric power steering systems face challenges in actively returning the steering wheel to a neutral position during straight driving, leading to uncomfortable steering experiences due to varying compensation currents and spurious viscosity friction, especially during turns.
Innovation Solution
An electric power steering apparatus that calculates a return control current based on the steering angle and motor angular velocity/Gr ratio, using a control section comprising a base-return control current calculator, target steering velocity calculator, return control gain calculator, limiter, and corrector to adjust the current command value, employing P-control, I-control, and D-control calculations to achieve smooth active-return control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electric power steering systems perform feedback control to accurately generate assist torque, then steering accuracy is improved, but the system cannot actively return the steering wheel to neutral position during straight driving
Solution Approach 1:
The control system is segmented into multiple independent control sections: a steering assist control section that handles steering accuracy through feedback control, and a separate active-return control section that handles the return-to-neutral function. This segmentation allows each control function to operate independently without interfering with the other, enabling both high steering accuracy and active return capability simultaneously.
Solution Approach 2:
A return control current calculation section is introduced as an intermediary component between the steering angle detection section and the motor drive section. This intermediary calculates and generates a return control current based on steering angle and vehicle speed, which is then superimposed on the assist torque control current. This intermediary mechanism enables active return functionality without disrupting the existing feedback control system's steering accuracy.
2Ease of operation
If return control current is increased to improve active-return performance, then steering wheel return capability is improved, but spurious viscosity friction and uncomfortable steering experience occur during turns
Solution Approach 1:
The return control gain is made dynamic rather than fixed. The control system calculates the return control gain in real-time based on the relationship between steering angle and vehicle speed. During turning maneuvers, when the steering angle changes rapidly, the system automatically reduces the return control gain to prevent spurious viscosity friction. During straight driving, when steering angle changes are gradual, the system increases the return control gain to improve active-return performance. This dynamic adjustment eliminates harmful friction while maintaining effective return capability.
Solution Approach 2:
The system changes the control parameter (return control gain) based on operating conditions. By monitoring steering angle and vehicle speed, the system adjusts the return control gain parameter dynamically. When detecting turning conditions through rapid steering angle changes, the gain is reduced to prevent harmful effects. When detecting straight driving conditions, the gain is increased to enhance return performance. This parameter change strategy resolves the contradiction between return performance and harmful friction.
3Ease of operation
If return control gain is increased to enhance active-return control, then return capability is improved, but excessive current output occurs during turns
Solution Approach 1:
The return control gain is dynamically adjusted based on real-time detection of steering conditions. During turning maneuvers, the system detects rapid changes in steering angle and automatically reduces the return control gain, preventing excessive current output. During straight driving, the system maintains higher gain values to ensure effective return capability. This dynamic control ensures that current output remains within appropriate limits under all operating conditions while maintaining good return performance when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system enables smooth active-return control by setting a suitable return control current, reducing the feeling of resistance and providing a reaction force corresponding to the steering angle, while limiting the return control gain to prevent excessive current output during turns.
Implementation Method 1
An electric power steering apparatus that energizes a steering apparatus of a vehicle by using a rotational torque of a motor as an assist torque
Implementation Method 2
a column shaft (a steering shaft, handle shaft) 2 connected to a steering wheel (handle) 1, is provided with a torque sensor 10 for detecting a steering torque Tr of the steering wheel 1
Implementation Method 3
a column shaft (a steering shaft, handle shaft) 2 connected to steered wheels 8L and 8R through reduction gears 3 (reduction ratio=Gr)
Data Source
AI summary
An active-return control section that calculates a return control current based on a steering angle, the vehicle speed and a motor angular velocity/Gr ratio, and drives the motor by a compensated-current command value obtained by subtracting the return control current from the current command value. The active-return control section includes a base-return control current calculating section that calculates a base-return control current, a target steering velocity calculating section that calculates a target steering velocity, a return control gain calculating section that obtains a deviation between the target steering velocity and the motor angular velocity/Gr ratio and sign-processes, and calculates a return control gain by at least two among a P-control calculation, an I-control calculation and a D-control calculation, a limiter that limits a maximum value of the return control gain, and a correcting section to output the return control current by correcting the control current with output of the limiter.